I have finished my song! 🎉
It's titled "Factory" because the keys sounds are from the EZKeys Dark Industrial expansion, and I chose a more raw metal-sounding kit for the drums (plus the user interface for the Dark Industrial expansion is really cool and looks like a steampunk keyboard). The guitar, bass guitar, and drums are all played by me, the only thing that isn't is the keyboard sounds (and looking at the MIDI files they're simple enough that I probably could manage to do most of them myself as well, but ehhh).
Really really happy with how this turned out, I did a bunch of reading and watching about how to EQ and master songs and the whole principle of making sure each instrument has its own space in the track and doesn't end mushing into other tracks and ending up muddy. I'm also very pleased that I once again didn't need to have flex-and-follow turned on on the guitar or bass to keep them in time, and the only tweaks I made to the drums were to fix just a couple of bits that weren't quite in time, to make a couple of the fills flow a bit better, and to slightly improve the feel of the final chorus at the end. And I didn't need to spend a ton of time re-recording the drums to get them right, it was probably only half an hour or so in total!